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I'd like to make a few comments about PFOs.

>I would be prepared to put quite a lot of money upon the fact
>that Kevin Gurr has a patent foramen ovale

PFOs are not the only risk factor for DCI, and indeed may not be a major
one. It is quite possible Kevin Gurr has one, but bubble-contrast
echocardiography would be required to be sure.

>and I would make sure that you dive at all times within the tables

Wilmshurst's study identified PFOs as a risk factor for DCI by finding a
higher than expected percentage of PFOs in divers who had been bent whilst
diving _within_ the tables.

It is worth remembering that the divers on whom the tables were tested
originally were never investigated for the presence of PFOs, and probably
as many of them had PFOs as the general population (or as the technical
diving community, for that matter). Two sets of tables is an interesting
idea, but of course would be extremely difficult (if not unethical) to
formulate.

>I'd also like to know how a PFO causes a problem on the arterial side
>when the normally fluid dynamics would seem to make this a remote possibility.
>Can you educate all of us?

Average pressure in the left atrium is normally higher than the right,
keeping the flap of tissue closed over the foramen. Pressure in the right
atrium can be raised by a number of factors, including transiently by
coughing, straining (e.g. lifting heavy equipment) and even just raisng the
legs if the person is lying supine. Under these circumstances bubbles
present in veins (often without symptoms but detectable by Doppler) can
cross to the left side of the heart, avoiding the filtering effect of the
lungs, and from there be carried to any part of the body. The medical term
for this is gas embolism.

As Chris suggested, divers with PFOs may suffer from a different spectrum
of DCI, as well as being more susceptible.

I'd happily answer further questions about this here or by mail if preferred.



Dr Andrew Pitkin
apitkin@ad*.de*.co*.uk*
apitkin@ci*.co*.co*.uk*

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